This invention relates to a strain-relief member for a two-conductor power supply cord attached to a personal care electrical appliance, such as a curling iron or hand-held dryer, and more particularly to such a strain-relief member which spreads the stresses of twisting (torsional strains) flexing and bending in the electrical cord thereby reducing likelihood of fracturing of the line cord.
Personal care electrical appliances often require replacement of broken power supply cords. This is probably because such appliances are so moved and rotated in use as to bend, flex, twist and pull the cord, putting great torsional strain on the cord, particularly at the junction where it is coupled to the appliance.
The problem of open circuited power supply cords in personal care electrical appliances such as hair dryers, has resulted in the establishment, by Underwriters Laboratories, Inc., of proposed new requirements for testing resistance to torsion of line cords used in personal grooming appliances. Under the test procedures, the sample being tested is mounted in a test stand with a quarter pound weight attached to the cord at a minimum of eight inches from the point of entry of the cord into the appliance. The test stand is designed to be alternately and reversingly rotated 540 degrees about the axial center of the cord. The proposed standard is that the cord must withstand a minimum of 10 cycles of 540 degree rotations clockwise and counterclockwise per minute for a total number of 1,000 cycles. If the cord breaks during this test, it is deemed unsafe.
Among the approaches which have been taken to prevent fracture from torsional stress is to provide a swivelling electrical connector between the appliance and the line cord, for example, U.S. Pat. Nos. 1,090,238; 1,762,422; 3,427,976 and 3,950,052.
The present invention represents a different solution and can often go through 6,000 test cycles without fracture.
Other strain-relieving techniques have been suggested. See, for example, U.S. Pat. No. 3,093,432. These, however, are directed to relief from bending, not torsional, strains.